1. Field of the Invention
This invention relates to an ignition timing control system for an internal combustion engine which uses a hybrid fuel containing alcohol.
2. Description of the Prior Art
For controlling the exhaust gases emitted by an automobile engine, it is a common practice to install a catalytic converter such as a three-way catalyst in the engine exhaust system. For coping with the fact that the catalysts including of this type of converter are inactive below a certain temperature, it is also a common practice to employ a system for quickly activating the catalyst after a cold engine start by retarding the ignition timing and thus quickly raising the exhaust gas temperature when the engine coolant temperature is low.
However, in such systems, a problem arises when the engine uses a fuel containing an alcohol such as methyl alcohol. Since the combustion temperature of alcohols is lower than that of gasoline, the temperature of the exhaust gas decreases with increasing alcohol concentration of the fuel. This slows the heating of the catalyst and thus delays its activation, with the result that the quality of the exhaust emissions is degraded.